What is the 2nd book of the Heroes of the Olympus about?

The book is called The Son of Neptune and is almost like the first book, The Lost Hero, in that Percy Jackson, yes he is back, gets trained by Lupa the wolf who trains all of the Roman Heros. It starts with Percy fight Medusa's sisters but he nor the gorgons will die. Then percy finds an old woman and carries her across the highway to a tunne with two Roman guards blocking it. Percy enters the tunnel and the two guards follow. They cross the Little Tiber, a river that protects the roman camp and was formally in Rome. The guards are Hazel and Frank. PS they are in Oakland, California. The three go on a quest to free Thanatos the god of the dead. On the way we figure out Hazel is the daughter of Hades and can make cursed stones lik diamonds and gold come out of the ground and Frank is son of Mars and his ancestor was an Argonaut. He can also shape shift into any animal. They go and free Thanatos and kill the Giant Alcyoneus. The Giant can only be killed out of his homeland of Alaska though. They three also recover the V cohorts golden eagle and many weapons that were lost when the V cohort went to Alaska on another quest in 1982. The the three return home the fastest horse called Arion and they get back to rome were Percy kills the giant meant to kill Poseidon. He kills him by using the statue of the minor god of boundaries. Then the romans kill off all of the others in the giants army. Percy because Praetor or leader of the camp and then right the end a huge war ship comes and Percy is just about to get on the book stops. The ship is from camp half-blood but no one knows exactly who is on it. THE BOOK IS A TOTAL CLIFF HANGER AND KNOW WE HAVE TO WAIT ANOTHER YEAR TO READ THE NEXT BOOK: THE MARK OF ATHENA.